The present invention relates to fabrication of fiber optic devices, and more particularly to a fabrication method that produces fiber optic devices having improved intrinsic resistance to external environmental conditions.
The widespread and global deployment of fiber optic networks and systems mandates that fiber optic devices and components operate reliably over long periods of time. This mandate imposes stringent performance requirements on various fiber optic devices and components that are used in such networks and systems. In this respect, since fiber optic devices and components are expected to operate reliably for decades or more, prior to qualification for use, such components are typically subjected to an array of mechanical and environmental tests that are designed to measure their long term reliability.
Guarantees of long term performance become especially crucial in application where the cost of failure is very high (e.g., submarine applications.) One of these tests is a damp/heat soak test, where a fiber optic device or component is exposed to elevated temperature and humidity conditions (typically 85xc2x0 C. and 85% relative humidity) for an extended period of time. Fiber optic couplers exposed to such conditions may exhibit a gradual drift in insertion loss. Eventually, this drift will cause a coupler to fail to meet its assigned performance specifications.
It is believed that the primary cause for the above-identified drift is water vapor or some component, constituent or by-product of water vapor diffusing into the exposed core glass of the coupler and changing the coupler""s index of refraction.
In an attempt to prevent migration of moisture into the coupling region, it has been known to provide improved packaging for optic couplers, with the goal of eliminating exposure to external environment. For example, prior art approaches have included packaging fiber optic couplers and other fiber optic components inside a metal tubing and sealing the ends of the tubing with a polymeric material, such as a silicon-based material or epoxy. These types of packaging have not proved successful in preventing the aforementioned problem.
Other prior art approaches have focused on reducing the introduction of water vapor during the manufacturing process. These attempts include the use of heat sources, such as a solid state heaters alone, that introduce less hydrogen/water during fabrication of a coupler, than is introduced using an xe2x80x9copen flamexe2x80x9d heat source. However, these attempts have also failed. Such approaches are deficient because it has been discovered that the introduction of water and water related species during fabrication is not a major cause of long-term drift of optical properties under damp heat accelerated aging conditions. See Maack et. al, Confirmation of a Water Diffusion Model for Splitter Coupling Ration Drift Using Long Term Reliability Data. See also, Cryan et al., Long Term Splitting Ration Drifts in Singlemode Fused Fiber Optic Splitters, Proc. Nat. Fiber Opt. Eng. Conf. Jun. 18-22, 1995.
In accordance with the present invention, there is provided a method of forming an optical device having a region treated by deuterium, comprising the steps of maintaining first and second optic fibers proximate to one another along a segment, and fusing together the segment to form a coupling region in the presence of a flame produced by combustion of deuterium gas.
In another aspect, the invention provides a method where the first and second optical fibers have different propagation constants.
In another aspect, the invention provides a method where a diameter of said first optic fiber is modified to change the propagation constant.
In another aspect, the invention provides a method where the diameter of one of the optic fibers is modified by heating the optic fiber while stretching the first optical fiber to reduce its diameter in a portion of the optic fiber.
In another aspect, the invention provides a coupler comprising at least two optic fibers having respective longitudinal segments, where the longitudinal segments are fused together in the presence of a flame produced by combustion of deuterium gas.
In another aspect, the invention provides a method where another chemical or compound is added to the deuterium fuel.
In another aspect, the invention provides a method where oxygen is added to the deuterium fuel.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and advantages of the invention will be realized and attained by the structure and steps particularly pointed out in the written description, the claims and the drawings.
The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:
FIG. 1 is a schematic diagram of a preferred embodiment of an optical fiber before stretching.
FIG. 2 is a schematic diagram of a preferred embodiment of an apparatus used to stretch an optical fiber.
FIG. 3 is an enlarged schematic diagram of a preferred embodiment of an optical fiber after a pre-taper operation has been performed.
FIG. 4 is an enlarged isometric view of a preferred embodiment of an apparatus and a coupler.
FIG. 5 is a graph showing change is splitting loss over time.
FIG. 6 is a graph showing median time to failure for various optical devices.
FIG. 7 is a chart showing probability distributions of rates of change of splitting loss at 85xc2x0 C./85%RH.
FIG. 8 is a table including data from TTF experiments.